The invention relates to a method for manufacturing a molded body. More specifically, the invention combines a core body of heat moldable hard foam material with a cover layer made at least partially of heat curable synthetic material. Such molded bodies may, for example, be made into wing blades for rotary wing aircraft and the like.
In the manufacture of bodies in accordance with the so-called sandwich type construction a support core or a base body is used which is made of a hard foam material such as polyvinylchloride foam which may be deformed while heated. The support core is covered by a cover layer of heat curable synthetic material, for example, synthetic resin including a fiber reinforcement. The cover layer and the support body are placed into a mold. However, when the cover layers are heated to their hardening or curing temperature it happened in the past that the support core was subject to a shrinking or further shrinking. Such shrinking caused the separation between the core and the cover layer at least in certain areas. Heretofore attempts have been made to avoid such separation by providing the core with an excess dimension prior to combining it with the cover layer. However, such excess dimension causes substantial difficulties when inserting the core into the mold and also in closing the mold.
It has also been proposed heretofore to preshrink the support core prior to its insertion into the mold. However, this approach is rather time consuming and additionally very wasteful in its energy requirements. For example, in preshrinking a support core of a rotor blade of a rotary wing aircraft experience shows that a preshrinking treatment of at least eight hours is required if a subsequent shrinking of the support core during the curing or hardening of the subsequently applied cover laminate is to be completely eliminated. Thus, preshrinking imparts an irreversible dimension to the core material.